Parallel-series hybrids

The larger battery will tend to impose thermal management problems on the system, which will require more complex monitoring, controls and hardware to maintain. Larger temperature spreads may result in premature degradation or possible thermal runaway situations, and even small but chronic temperature differences will require more frequent equaUzation. 

While the technological problems are reeognizable, it is also important to note that, at the battery size that will produee an appropriate amount of energy, sendee due to lower quality will be readily cost-apparent to the customer and vehicle 

Event Power Time Voltage limits (approximate) Temperature Cycles (10 y) 

General requirements. The attributes in Table 11.20 are typical for parallel hybrid applications, and the attributes in Table 11.21 are typical for series hybrid vehicles. 

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Fig. 11.19. Typical parallel-series hybrid battery architecture. Ground and communications to devices external to battery system not indicated.

Controls and diagnostics for parallel-series hybrid vehicles. A typical set of control messages for hybrid vehicles is listed in Table 11.19. Although the variables are the same as those used in soft hybrids, the higher criticality of function implies that the calculated values, such as maximum source and sink currents, must be of even higher reliability if unexpected function fade or failure is to be avoided. 

VRLA as a parallel-series hybrid battery. The high utilization of the hybrid battery predisposes sourcing to batteries that cycle extraordinarily well. Without question, flooded lead-acid batteries should not be considered, and despite a reasonable cycling ability, even VRLA is less than well suited for hybrid duty unless the VRLA battery is greatly oversized. 

The cost dependency on a minimized cell size for Ni-MH and VRLA batteries is shown in Fig. 11.21. In these cases, VRLA is limited by life and Ni-MH is limited by power. At the energy levels required for parallel-series hybrid vehicles, it can be shown that the watt-hour life cost of Ni-MH would have to exceed 33 times that of VRLA, which is not the case even today with prototype batteries. The initial cost consideration that tipped the favour to VRLA for soft hybrids is far less impressive with parallel or series hybrids, since it can be further demonstrated that, even on an initial cost basis, VRLA is about 60% of the cost of the equivalent Ni-MH battery for the parallel-series application, well outside of the bounds where trade-off to initial cost could be considered. 

In two further articles, Olteanu and Pavel (1996, 1997) combined the dissociation model ofDanek(1989) with the series and parallel models of Fellner (1984) and proposed sophisticated series-dissociation, parallel-dissociation, and series-parallel-dissociation hybrids. It should be pointed out that the small improvement in the fit with experimental data is attained by introducing further variables. The standard deviation of the fit, however, should always be compared with the experimental error of measurement. 

The basic configurations for HTEVs aie the series hybrid and the parallel hybrid, which are shown in the Figs. 5.17 and 5.18, respectively [1]. In the series... 

High-voltage safety considerations require that the architecture of parallel- and series-hybrid vehicles include an integral BMM such that the battery can be controlled from within the pack. This assumes that the battery will be of an advanced design, such as Ni-MH, where safety requires fast, reliable, and self-contained communication with the contactor and charger. 

Figure 7.2 Schematics of (a) series-hybrid (b) parallel-hybrid (c) layout of power-train components.

Figure J6.4 Series hybrid (a) and parallel hybrid (b) for fuel-cell hybrid vehicle. Reproduced from [14].

Figure 36.12 gives an overview of series fuel-cell hybrids that fulfill these assumptions. In the first step, they are divided into two groups passive fuel-cell hybrids and active fuel-ceU hybrids. Active series hybrids may have between one and three DC-DC converters. In the case of two or three DC-DC converters, they can be arranged in a parallel fashion or in a cascade connection. 

FCVs are special as they have electrical power transmission, whereas a hybrid vehicle may be a combination of electrical and mechanical power transmission. Hybrid vehicles are further categorised as FCV with parallel hybrid power circuit and FCV with series hybrid power circuit as shown in Figs. 9.4 and 9.5, respectively. 

As shown in Fig. 9.4, in parallel hybrid power circuits the fuel cell delivers power to the motor and charges the battery when required. It also provides extra power to the motor for acceleration once the battery is fully charged. In the case of a series hybrid power circuit, all the power is delivered by battery so it needs to be large. The function of the fuel cell is only to charge the battery depending on driving conditions it can be of relatively low power. Such vehicles generally use alkaline fuel cells. 

The control strategies for dual mode hybrid vehicles are a combination of those used for series and parallel hybrids. There are so many possible hardware arrangements and associated control strategies, it is not possible to summarize them in a simple manner as was the case for series and parallel hybrids. The objective of the dual mode operation is to use the... 

The fuel economy of series and parallel hybrid vehicles are compared in Table 3 for both the com-... 

Comparisons of the Fuel Economy for Series and Parallel Hybrid Vehicles (1) Fuel economy shown lor diesel engines is gasoline equivalent... 

Figure 5. Configuration of hybrid corona reactors (A) series and (B) parallel.

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